Easy Parenting: Brood Parasites Get Someone Else to Do the Hard Work

Friday, September 25th, 2020 | Petrina Duncan | No Comments

 For most birds, reproduction is a life process that takes up a lot of time and energy. There are huge energetic costs to a female bird with respect to mating, egg-laying, incubating the eggs and feeding hungry chicks for many weeks or months. Some birds also migrate vast distances across land and sea before breeding can commence, using up even more time and energy. Breeding for a bird is a lot of hard work.

So, if a bird found an easier way to become a successful breeder, we would expect that behaviour to be favoured by natural selection and become fixed. In about 1% of all bird species, that’s exactly what has happened: it’s called brood parasitism.

Brood parasites are birds who have learned how to make the parenting process much easier. They still have to find a partner and mate successfully, but instead of the female bird laying her eggs in a nest that she and/or her partner made, she stealthily lays them in the nest of another bird. Intraspecific brood parasites lay eggs in nests belonging to birds of their own species, compared to interspecific brood parasites who target other bird species.

Common cuckoo chick in the nest of a tree pipit.

Common cuckoo chick in the nest of a tree pipit.








Benefits and advantages for the brood parasites:

  • Increased breeding output
  • Minimal energy expenditure because they don’t defend a nest, incubate eggs or feed chicks.
  • Genes passed on to the next generation.

Costs and disadvantages for the host birds:

  • Decreased breeding output
  • Expending more energy raising someone else’s offspring, especially if the parasitic chick is very large as more food will have to be found.
  • Not passing on genes to the next generation.

Generalists and Specialists

Some brood parasites put their eggs into the nests of a wide variety of other species. These are called generalists. An advantage of this behaviour is the flexibility it offers. Generalists can be successful in many different places and at almost any time, as long as a suitable host bird is nesting nearby.

Alternatively, brood parasites can be specialists. They will target one species to be the host of their egg/s. The limiting factor in this approach is the lack of flexibility, as parasites must live close to their host species or spend time and energy travelling to find them during the breeding season.

 Brood parasites in New Zealand

Cuckoos are the most famous brood parasitic birds worldwide. In New Zealand, two migratory species of cuckoos arrive on our shores in September and October each year. The shining cuckoo/pīpīwharauroa (Maori name) is the smaller of the two species. These small birds fly all the way from the Solomon Islands and the Bismarck Archipelago, a distance of more than 5000 kilometres. On arrival in NZ, shining cuckoos/pīpīwharauroa seek out their target host species, the tiny grey warbler/riroriro, in forests and gardens across the whole country.

Shining cuckoo/pīpīwharauroa being fed by its host parent, a grey warbler/riroriro.

Shining cuckoo/pīpīwharauroa being fed by its host parent, a grey warbler/riroriro.










Long-tailed cuckoos/koekoeā fly to NZ from even further away. They spend winter in an arc of Pacific Islands which extends from Henderson Island (Pitcairn group) in the east to Palau in the far west of Micronesia. A long-tailed cuckoo/koekoeā migrating from Palau to NZ will fly more than 6700 kilometres – perhaps that’s why they don’t have the energy to be a ‘normal’ bird parent. They arrive in NZ in September and October to begin searching for their target host species. In the North Island, they look for a small bird called the whitehead/pōpokatea in tall, mature forests. The forests of the South Island have two host species for long-tailed cuckoos/koekoeā: the brown creeper/pīpipi and the rarer yellowhead/mohua. All three of these host species are endemic to NZ and closely related.

Whitehead host parent feeding a young long-tailed cuckoo

Whitehead host parent feeding a young long-tailed cuckoo












Strategies of a successful brood parasite

  • Be selective. Brood parasites take their time to find the best host ‘mum’ to be a surrogate parent for their offspring. In human terms, this is a like parents shopping around to find the very best day care centre for their toddler. Before putting her eggs into a host’s nest, the parasitic bird will watch a potential ‘mum’ closely to appraise her age, condition, singing ability, territory location, size of the nest and its location. These factors will contribute to the parasite’s final choice of the best host for the job.
  • Team Work. Some parasitic bird pairs work together to achieve their goal. For example, male great spotted cuckoos in Southern Europe will stage an attack on an unsuspecting pair of magpies. The male cuckoo appears in full view of the magpies to divert their attention and launch a pretend attack. Meanwhile the female cuckoo sneaks into the magpies’ nest to quickly lay her egg. This risky egg-laying behaviour is only possible because both the male and female are working as a team to ensure the hosts don’t see what’s happening.
  • Egg mimicry and timing of laying. Parasitic bird eggs have evolved over time to look and feel very similar to the host’s eggs, a concept called egg mimicry. This reduces the chance of egg rejection by the host. Their eggs also usually have thicker shells than the host’s eggs. Parasitic birds will also strategically time their egg laying. By waiting until the host has already laid a few eggs, the parasitic female ensures that incubation is already underway.
The larger blue egg is that of the parasitic common cuckoo. The cuckoo’s egg looks very similar to those of the host, a common redstart

The larger blue egg is that of the parasitic common cuckoo. The cuckoo’s egg looks very similar to those of the host, a common redstart










  • Chicks who are bullies. Brood parasite eggs generally hatch earlier than the host’s eggs. The parasitic chicks use strategies like pushing the host’s eggs and chicks out of the nest or stabbing chicks with a special hook on their beak. Imposter chicks also tend to make louder, more frequent begging sounds to ensure they get all the food from host parents. Some species like NZ’s shining cuckoo have chicks who can mimic the begging call of a grey warbler’s chicks, ensuring the host is fooled into feeding them.
  • Total destruction of eggs. Sometimes a cuckoo misses the chance to lay her eggs at the optimum time. As an extreme measure, she will destroy the entire egg collection in the host’s nest. This behaviour is like a reset for the host bird to start over with breeding. She will probably mate again and lay another clutch of eggs while the watchful parasite bird prepares to intercept at just the right time.
Common cuckoo chick in host nest

Common cuckoo chick in host nest











Can host birds fight back?

Brood parasitism is a classic coevolutionary “arms race”. Each time a host species evolves a new behaviour to defend against brood parasitism, the parasite species evolves a new trait which makes its breeding strategy more successful. Here are a few ways in which hosts can fight back.

  • Egg recognition. Many host birds have evolved to be experts at egg recognition. They will recognise and then reject eggs which look different to their own. Sometimes a host will even leave its nest entirely if a strange looking egg appears. However, brood parasites have adapted to this selection pressure by either becoming generalists (they parasitise multiple species) or producing eggs which are almost identical to the host’s eggs (egg mimicry).
  • Chick recognition. Some host ‘mums’ are able to recognise and reject chicks which are not their own. However, rejecting chicks carries the risk of mistakenly rejecting their own chicks. If the rate of parasitism is very high, selection for accurate chick recognition will be stronger.
  • Nest features. Species that commonly get parasitised may deploy nesting tactics to minimise interference. Their nest may be well camouflaged to avoid detection. The nest’s location could be away from places where parasitic birds can sit. The nest entrance may be too small for the brood parasite to enter. For example, the grey warbler’s nest entrance is tiny, preventing shining cuckoos from entering. But the cuckoo manages to parasitise their nests regardless. Researchers suspect the egg is laid elsewhere then carried in the cuckoo’s beak up to the warbler’s nest and carefully deposited inside.

Should we be concerned about brood parasitism?

As our climate changes and the human population continues to increase, natural habitats such as forests are disappearing due to fires, logging, agriculture and urban sprawl. For bird species that are already in decline due to habitat loss, brood parasitism  may pose a significant threat, especially if generalist parasites increase in numbers. Reproductive success will be compromised at a time when the population is already decreasing. The combined pressures could become too much, putting the species at risk of localised extinction.

On the bright side, a brood parasitic species can’t survive without its host species. Parasitic birds often wait until their target host has raised one clutch of offspring before parasitising the second nest. This is a behaviour which will give rare host species a helping hand.

Grey warblers will often raise a family of chicks successfully early in spring, before the shining cuckoos arrive in NZ from their long migratory journey. Even if the grey warbler’s second nest gets targeted by a shining cuckoo, they have already contributed their genes to the next generation and hopefully the behaviour of early nesting was also passed on to their offspring.

For rarer NZ bird species such as the yellowhead/mohua and whitehead/pōpokatea, being less successful breeders due to parasitism by long-tailed cuckoos/koekoeā is a concern to conservationists. Long-tailed cuckoos are also able to parasitise the nests of the more common brown creeper/pīpipi in the South Island. As yellowhead numbers decrease, brown creeper numbers may also begin to decline due to being parasitised at a higher rate. In the North Island, whiteheads are increasing in numbers due to human conservation efforts which will hopefully help to mitigate the negative effects of brood parasitism.


Brood parasitism represents a rare and unusual parenting strategy. There are many benefits for the bird who does the parasitising such as avoiding most of the hard work involved with being a parent.

Brood parasitism is a great example of coevolution in which the evolutionary “arms race” is played out in the privacy of a nest or within the boundaries of a territory. There will always be winners and losers in this host-parasite exploitative relationship. What we must try to do is reduce or eliminate human-related pressures which adversely affect the breeding success of birds. By helping to conserve native bird species and their habitats, we’ll be supporting them to withstand the negative impact of brood parasitism long term.

Further reading:

Photo Credits:

Common cuckoo chick in the nest of a tree pipit.
Vladlen666/WikiMedia Commons (CC1.0)

Shining cuckoo/pīpīwharauroa being fed by its host parent, a grey warbler/riroriro.
Photography by Robin Colquhoun. From NZ Birds Online: http://www.nzbirdsonline.org.nz/species/shining-cuckoo#bird-photos

Whitehead host parent feeding a young long-tailed cuckoo. Photography by Adam Clarke.
From NZ Birds Online: http://nzbirdsonline.org.nz/species/long-tailed-cuckoo

The larger blue egg is that of the parasitic common cuckoo. The cuckoo’s egg looks very similar to those of the host, a common redstart. Photography: Dr. Tomas Grim. https://phys.org/news/2018-05-russian-cuckoo-invasion-alaskan-birds.html

Common cuckoo chick in host nest. Photography by Per Harald Olsen (CC BY 2.0)

Study Skills, Exam Revision and Time Management

Friday, June 26th, 2020 | Petrina Duncan | No Comments

Student sitting meditatively on pile of booksRevising for exams is a task that most students dread. It’s that daunting time when you suddenly realise that there is a lot more information to learn than days left to learn it all. Often, many other events are going on in your life at the same time, so revision gets left until the last minute, which only makes things worse. As your stress levels build, you may find it difficult to sleep or lack the energy to exercise. Ultimately, you need to monitor your own stress levels and take control over when and how your revision gets done.

If there is one piece of advice to give, plan ahead. It’s never too early to start getting organised for assessment. With a clear plan for each of the subjects you’re studying, you will have more confidence and a sense of purpose. You’ll know what the end goal is, how long you have to get there, and all the steps needed on the way to achieving success.

For school students, you’ll probably have some practice exams coming up during Term Three. These exams are often shorter in duration than the final exams because you haven’t yet covered all the topics for the year’s work. Find out from your teachers exactly what will be examined in the practice exams. Then find out when these exams are and make a plan going backwards from exam week to now.  Consider using a planner template to plan when you will revise each subject. You can also add in other commitments such as sports practice, hobbies and leadership roles. You may have other deadlines such as internal assessments, practicals and sports competitions coming up, all of which should be added to your planner.

Identify when you have time each day to study for the exams. It might be a slot between 4pm and 6pm each week day, or a Saturday afternoon. For each subject you study at school, allow at least three hours of study time per week. As exams get closer, increase the number of hours per week. Remember to include breaks, sport, relaxation and fun in your schedule. Avoid too much computer time, especially just before bed. If you are lacking motivation, think about creating a study group with a few friends. Getting together for a focused session for one hour might be more worthwhile than sitting alone at home all evening getting distracted by social media. You could even teach each other part of a topic. Most of all, keep eating well, get plenty of sleep and exercise, and monitor your stress levels.

Revision can be broken down into four phases:

  1. You’ll need to do an initial reading of the content of a topic. After reading, try writing a summary (from memory) of what you have read. Organise the summary in a way that works for you, such as in mind maps, wall charts, flash cards, voice recordings or flow charts. Go back to check that your original notes match your summary – add in any forgotten information.
  1. Next you should read your summary over and over again for the next few days. Test your knowledge by forcing yourself to say it out loud, make links between parts, do quizzes, draw diagrams, write paragraphs or write definitions. Stick notes onto the wall of your room so that you see them daily. Your aim is to move the information into your long term memory.
  1. Monitor your ability to recall/understand certain aspects over others. Which bits do you keep forgetting? Try another way to remember those things. Keep reading over your notes and summaries. Test yourself again. Ask a friend/relative to help with testing you. Do more quizzes or multi-choice tests … try Kahoot online.
  1. Finally, practise answering past exam questions. NZQA subject resources can be found here. Become familiar with the way exam questions are worded for each subject. Be aware of which topics have been asked in the last three years of exams. If parts of questions such as graphics or photos are missing from the website versions of exams, ask your teachers if they have a paper version that you can photocopy. Mark your work using online assessment schedules. Give your work to your teacher for feedback and ask if you can spend some time going over their suggestions after class.

At this point, forming a small study group would be worthwhile. You could all attempt a past exam paper, then meet up to discuss your answers and mark each other’s work. Talking about the parts you struggled to answer will help your understanding greatly. Find out how your friends are doing their revision. Swap ideas and share your knowledge. Keep it fun!

Finally, always put your phone in another room when you are studying. It is just a distraction. Use it as a reward for an hour’s solid study when you take a break. Good luck with your revision!


TKI  study and Exam techniques


NZQA Subject Resources

Phases of revision (Massey University, NZ):

Revision tips



Mind Mapping – Why you should be doing this.

Thursday, March 12th, 2020 | Petrina Duncan | No Comments

You might have heard of mind mapping. Perhaps one of your teachers or lecturers asked you to make one for a complicated topic. Maybe you scribble them on paper regularly when you’re trying to make sense of something complicated. Or it’s even possible that you’ve missed the mind mapping bus altogether. In this month’s blog, you can learn about what mind maps are, why they could be useful to you and how research has proven their benefits for higher education.

What is a mind map?

We can define a mind map simply as ‘a graphical way to represent ideas and concepts’(1) or ‘a creative and logical means of note-taking and note-making that literally “maps out” your ideas’(2). Both of these descriptions should paint a picture in your mind of words and ideas splayed out across a page in a meaningful visual way. Mind maps also comprise a network of connected and related concepts(3). They are not just random words thrown together on a page. At the core of a mind map is a central idea, topic or issue. Splaying out from that central topic are a number of subtopics, and branching off those are more notes or diagrams. Lines may also be used to connect different branches of the map to show links between ideas, concepts or subtopics.

Example of a mind map about how to stay focused in a digital world:

Example of mindmap on how to focus in age of distraction

Image from: http://learningfundamentals.com.au/resources/ (4)

As you can see in the mind map above, the creator(4) has chosen a cartoon-like approach with colours, graphics and words to illustrate their ideas about how to stay focused. This mind map would be useful to refer to regularly as a good reminder when you’re not focused.

The most important thing to remember is that a mind map is yours, not anyone else’s. You create it in your own way to visually represent information that is in your mind. No one can tell you that your mind map is wrong, because they can’t see inside your brain where your thoughts and neurons are firing rapidly during the mind mapping process. This map is made by you, for you, in order to safely navigate the often confusing situation of being swamped with too much information. By the time you have made a mind map, you will probably find that your brain has done a download of some (or all) of that information, leaving you free to focus on other things or to take action.

As a demonstration of how mind mapping can work, at least for me and my mind, I decided to choose a topic that I haven’t had to think about for 26 years but which most senior school students will be thinking about all the time: going to university. It’s completely normal to start thinking about university in your last year or two of school. The problem is, as soon as you think ‘university’ you start to think about all these other things like degrees, money, deadlines, careers, scholarships, applications, hostels, etc. All of a sudden, you may start to feel a little overwhelmed because you know almost nothing about anything related to university, yet you feel like you should know more. It may all become too hard, so you do nothing, hoping it all sorts itself out. But it won’t. No one else is going to do the work for you this time. Getting to university is up to you. So instead of sticking your head in the sand, take a deep breath, pick up a pen and try making a mind map.

Here is a rough draft of a mind map that I made in about 20 minutes, as if I was thinking about going to university for the first time next year, in 2021:

Mind map on How to a organise going to University

If I was making this mind map for my future use, next I would colour it in and draw lines between parts that link together, but I didn’t want to make it too messy for you. The only resource I used to make this map was a University of Otago Undergraduate Prospectus booklet(5) which contains essential reading for about-to-be-first-year students.Image of front cover of 2020 Undergraduate prospectus

Back in the 1990’s, before internet searches existed, the Prospectus booklet was the only source of information for planning a university degree. Now, there is so much information out there online that it can be confusing, but the Prospectus should still be your go-to booklet for university planning because it has everything in one place. If I was heading to university next year, I would keep referring to my mind map and work my way through all the things I needed to research and do. I could even make other mind maps which branch off from this one, focusing on ways to make money for university, the pro’s and con’s of each university or which course to take.

The sky is the limit with mind maps!

So, are there other advantages of using mind maps to organise information, other than just to do a ‘download’ from your busy mind? Yes. Here are some of the additional benefits:

  1. Mind maps can help you to break down complex information and issues, making them easier to understand.(4,6)

When something seems really complex, a mind map helps you to simplify information into some kind of logical picture that your brain can make sense of. Think about a topic which you struggled with in your last year at school. If you’d made some mind maps, could you have presented the information to yourself in a way that was less confusing and more clear? Would that have made it easier to see links between topics and subtopics, or between different concepts?

For example, climate change and global warming are complex issues facing our planet and society at the moment. The simple mind map below(4) shows one way of organising some of the key science ideas about global warming in a way which looks interesting and less complex. You can also see clear links between certain aspects, such as the different greenhouse gas emitters or before/after the 1750 industrial revolution. From this simple outline of the main ideas, you could do more research then write a report or essay about the whole topic.

Image from:  http://learningfundamentals.com.au/resources/ (4)

  1. Mind maps improve memory and recall(6)

Our brains easily remember images that we have seen which can then link to other memories. How often have you looked at an old photo of yourself, then suddenly remembered lots of other things which happened during that event? It is generally easier to remember a diagram than a description(3). For example, in an exam, you could quickly sketch the global warming mind map again which you had made earlier in the year or when you were studying. The diagrams and lines in the mind map would then jog your memory of the main ideas for a well-structured essay. Easy!

As a trial, try taking a topic that you have already studied this year and creating a mind map of it. You could either do this using notes or just from memory. Afterwards, pull out your textbook and see what you’ve missed. Add more content, links, diagrams, colour etc, until it summarises all the important key things for that topic. Use it regularly to remind yourself of what was covered during that topic and again for revision.

  1. Mind maps are a more engaging style of learning(6)

Have you ever spent a whole class period copying notes off the whiteboard or projector screen? If yes, did that method help you to learn? Some learners would say yes. However, a different style would be to create a mind map to brainstorm student ideas of what you already know about a topic or issue, to connect ideas together and work in a group to share ideas between students. This active process would engage everyone in the group, whether they are sharing their ideas or writing on the paper. Talking would generate more ideas. Between you, a whole-page mind map could be created and then shared with the teacher and class. This would be collaborative and engaging, much more so than copying down notes. And you’d be more likely to remember it all too! A scan or photocopy of the final mind map could be taken and shared.

  1. Mind maps help to show connections between existing knowledge and new learnings

This process is sometimes called ‘meaningful learning’ – making links between prior knowledge and new knowledge(6,7). This process doesn’t always happen by itself, especially when you are young. Mind mapping can help to create meaningful learning if students are forced to find connections between their existing knowledge and new learnings.

For example, take a topic like micro-organisms. If you had to make a mind map now, based on your current knowledge of micro-organisms, what would it look like? How much do you know and how would you organise those ideas on a page in a visual way? Next, imagine if you did a week or two of learning about micro-organisms, either in biology class or doing your own research. If you then took your original mind map and had to add some of your new knowledge to it, the process of doing so would force you to think about integrating and connecting the old and new information in a meaningful way(7) so that the mind map still made sense to you.

Along comes a pandemic like COVID-19 (novel coronavirus). How could you connect that into your micro-organisms mind map? Is it a virus, bacteria or fungi? Will it be helpful or harmful to humans? How and why does it spread? You can see how having one mind map is a good starting point but soon your mind will want to make more of them, branching off the first one. This is a visual representation of you learning and processing new information. Imagine if you took your original mind map to your teacher and said “I decided to add my new knowledge about the novel coronavirus to the mind map that we made in class last week – can you please give me some feedback?” You would make your teacher’s day!

In summary, mind maps are a meaningful learning tool and are definitely worth trying out if you haven’t already. There are lots of free mind mapping websites which are fun to try out: simplemind.eu, mindmeister.com, mindmup.com, sciencemindmaps.com, xmind.net, coggle.it, mindmapping.com and there are some instructions at simplemind.eu which are worth reading(8). Try drawing your own mind map on paper first. The creativity feels great and you won’t be constrained by using any particular template. Good luck – enjoy the mind mapping journey ahead!

Links to references:

Petrina Duncan- Science Teaching Coordinator